Discovery of volcanic ash bed from the basal Subathu Formation (Late Palaeocene-Middle Eocene) near Kalka, Solan District (Himachal Pradesh), Northwest Sub-Himalaya, India

摘要

Discovery of 1.5 m thick volcanic ash bed is reported from the basal part of the Late Palaeocene–Middle Eocene Subathu Formation exposed along the Koshaliya river near Kalka (Solan District) in the foothills of Himachal Pradesh. The ash bed represents the oldest volcanic ash horizon from this part of the Himalayan Foreland Basin. The ash is fine-grained and consists mostly of kaolinite with trace quantities of glass shards, euhedral and angular beta-quartz, sanidine, zircon, biotite and anatase. Ithas high concentrations of Al2O3 as well as incompatible elements (Zr, Nb, Th and Y), and high loss on ignition. Based on lithological as sociation, field characters, mineralogy and geochemistry, the ash bed has been identified as tonsteins of a volcanicorigin. The stratigraphic position and thickness of the ash bed indicate a significant volcanic event during the Early Eocene.